Project Summary Advancing age is a primary risk factor for the development of cardiovascular disease, and this is primarily attributable to the development of vascular dysfunction, including increased large elastic artery stiffness. Current demographic trends predict a major increase in the population of older adults. Therefore, a top biomedical research priority is to identify strategies that preserve vascular function and maintain low arterial stiffness with advancing age, as this may help prevent, reduce, or delay the development of CVD. Age-related arterial stiffness involves major structural changes to arteries, but mechanisms underlying these structural changes are incompletely understood. A compelling hypothesis is that excess mitochondria- derived reactive oxygen species (mtROS) in the vasculature may play a key role. With advancing age an increase in mtROS drives a vicious cycle of mtROS-induced mitochondrial dysfunction which may promote age-related arterial stiffening via induction of chronic inflammatory signaling. Thus, reducing mitochondrial oxidative stress and dysfunction may be a promising therapeutic target for arterial stiffness with aging. The central hypothesis of this project is that a mitochondria-targeted antioxidant (MitoQ) may be a novel therapeutic option for treating and/or preventing age-related arterial stiffness by reducing mtROS--and consequent mitochondrial dysfunction and inflammatory signaling-in the vasculature. Specific Aim 1: To assess large elastic artery stiffness before, during, and following treatment with mitochondrial antioxidants administered in the drinking water. Old mice will be tested before and after short- term (4 weeks) mitochondrial antioxidant therapy to test the hypothesis that treatment will reduce arterial stiffness (Aim 1.1), whereas middle-aged mice will be tested before, during and after long-term (9 months) therapy to determine the potential for treatment to prevent increases in stiffness with advancing age (Aim 1.2). Specific Aim 2: To determine changes in structural components and markers of inflammation in arteries of mice with aging and MitoQ treatment (Aim 2.1); to comprehensively assess changes in mitochondrial function (including novel assessment of respiratory function) in the arteries of mice with aging and MitoQ treatment (Aim 2.2); and to examine the role of mitochondrial oxidative stress and inflammation in mediating arterial stiffness by assessing intrinsic stiffness and structural changes in arteries from young and old mice following treatment with modulators of mtROS production and/or inflammation (Aim 2.3). Overall, this project will: a) establish the efficacy of mitochondrial antioxidants for the treatment and/or prevention of age-related stiffening of large elastic arteries; b) provide the necessary pre-clinical evidence to support the translation of mitochondrial antioxidant therapy to humans; and c) provide novel insight into the role of mtROS in the development of age-related large elastic artery stiffness, and the mechanisms whereby aging and/or antioxidant treatment may alter vascular mitochondrial physiology.